The wide-spread development and adoption of promising interventions for substance abusing criminal justice clients (e.g., diversionary programs and psychopharmacological treatments) has led to a proliferation of controlled studies to establish their efficacy. The expansion of this type of research raises concerns about whether we can ensure autonomy and minimize perceptions of coercion to participate in research within this doubly vulnerable population. Despite numerous institutional and federal requirements aimed at ensuring the autonomy of vulnerable research participants, the field lacks a reliable and valid way of measuring perceived coercion to participate in research. In response to this need, we developed and have begun to evaluate the Coercion Assessment Scale (CAS), an instrument that focuses specifically on coercive pressures that may be experienced by substance abusing offenders asked to participate in research. Preliminary findings from three prior studies have revealed promising levels of internal consistency and convergent and discriminant validity. The proposed study seeks to further develop the CAS as a comprehensive, reliable, and valid instrument for measuring coercion to participate in research among substance abusing offender populations. The study will proceed in three phases. Phase 1 involves conducting focus groups with clients and professionals to develop a larger item pool that more fully captures the construct of research coercion. Phase 2 involves a protocol analysis of the beta instrument to ensure that items are correctly understood by participants and to improve their wording. Phase 3 involves establishing the psychometric properties of the finalized instrument including item response properties, test-retest reliability, internal consistency, factor structure, convergent validity, and discriminant validity. Development of the CAS responds to the need for an instrument to accurately measure perceptions of coercion among substance abusing criminal justice clients participating in research. Much like consent quizzes and tests of cognitive functioning, the CAS will be useful for identifying individuals who may not be appropriate for research participation because of their level of perceived coercion. In this context, the CAS may be particularly useful to research staff, research intermediaries, and IRBs. In a more academic context, the CAS will provide a reliable and valid way to measure changes in perceived coercion in the development of new strategies for improving consent and recruitment procedures and reducing potential harms to human research participants. PUBLIC HEALTH RELEVANCE: Development of the Coercion Assessment Scale (CAS) responds to the need for an instrument to accurately measure perceptions of coercion among substance abusing criminal justice clients participating in research. Much like consent quizzes and tests of cognitive functioning, the CAS will be useful for identifying individuals who are not appropriate for research participation because of their level of perceived coercion. In this context, the CAS may be particularly useful to research staff, research intermediaries, and ethics review boards.